Silicates mixed anion

Heidebrecht, K., and Jansen, M. (1991) Agig(Si04)2(Si40i3), the first silver silicate with mixed anions, Z Anorg. Allg. Chem., 597,79-86, (1991) 606,242. 

Binary rare earth borates 216 4.8. Mixed anion silicates 276... 

Despite the fact that silicate-phosphate glasses showed some unexpected toxic influences, there are many other mixed anionic systems worthy of study. The borate-phosphate systems have been studied to a small degree. Some work has been done on sulfate-phosphate systems. Thilo s group studied the arsenate-phosphate and stibnate-phosphate chemistries in great detail, but very little applied work was done. This was probably a result of the mild toxicity of these systems. 

Asphalt emulsions are dispersions of asphalt in water that are stabilized into micelles with either an anionic or cationic surfactant. To manufacture an emulsion, hot asphalt is mixed with water and surfactant in a colloid mill that produces very small particles of asphalt on the order of 3 pm. These small particles of asphalt are prevented from agglomerating into larger particles by a coating of water that is held in place by the surfactant. If the asphalt particles agglomerate, they could setde out of the emulsion. The decision on whether a cationic or anionic surfactant is used depends on the application. Cationic stabilized emulsions are broken, ie, have the asphalt settle out, by contact with metal or silicate materials as well as by evaporation of the water. Since most rocks are silicate-based materials, cationic emulsions are commonly used for subbase stabilization and other similar applications. In contrast, anionic emulsions only set or break by water evaporation thus an anionic emulsion would be used to make a cold patch compound. 

Upon gel formation after mixing the silicate and aluminate solutions the liquid phase still produced the bands attributed to the initially present silicate and aluminate anions, but these were much lower in intensity. Throughout the induction the intensity of these bands remained constant... 

The most plausible interpretation of the above results is as follows Al in aluminate solutions is present in the form of AKOH) anions irrespective of the Al concentration or the Na/Al ratio (150,181,182). When solution A, containing low molecular weight silicates and thus a high proportion of reactive SiOH groups, is mixed with the aluminate solution, a predominantly aluminous intermediate results. When, by contrast, solution B, richer in silicon and with fewer silanol groups, is used, a silca-rich intermediate is formed. But the composition of zeolite A (with Si/Al = 1.00) is achieved via structural rearrangements in the amorphous precursors and is dictated by the final structure itself. 

New developments in the use of silicates to improve flame retardancy have arisen from the use of synthetic anionic clays that correspond to the family of lamellar mixed metal hydroxides, commonly named layered double hydroxides (LDH) or hydrotalcite-like compounds.17... 

TMS esters are the derivatives of oxygen-containing anions that have been applied most frequently to GC analysis. They were first applied to the analysis of silicates [582], Further, the method was developed for the analysis of five silicates in siliceous rocks [583], as follows. A 20-g amount of powdered sample was added to a mixture of 125 g of ice, 150 ml of concentrated HC1, 300 ml of 2-propanol and 200 ml of hexamethyl-disilazane, which had been stirred for 1 h. The complete reaction mixture was then stirred for 16 h at room temperature. After filtration the silazane (upper) layer was separated, washed with water, mixed with 2.5 g of Amberlyst 15 for 1 h, filtered and stripped at 115°C. The liquid residue in the distillation flask was analysed on a column packed with SE-30 with temperature programming. 

The synthesis of the pentavalent mixed halogen silicate anion was achieved in part as well. The reaction of CsCl with SiF yielded the SiClF anion, for example, and the series was extended up to and including the SiCli,F anion. However, attempts to synthesize the SiCls anion with either the Cs or K cation were unsuccessful. This may indicate that either this anion is not stable, contrary to one pi iblished report, or that there is some inherent limitation to the salt/molecule technique. This point will be discussed in more detail below. 

A useful method for the separation ofhydrazoic acid is by a column extraction technique using a mixed-bed ion-exchange resin, a strongly acidic resin in the [H form], and a weakly basic resin in the (OH" form). All cations and most anions are held on the column while hydrazoic acid runs through the column. Other cations and anions elute as water. Weak acids, e.g., boric, silicic, and carbonic will also run through the column. The technique has not been applied to the analysis of explosive azides however, it has been used for the analysis of alkali azides and for the preparation of standard solutions of hydrazoic acid [18]. 

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